Recent years have seen an increase in active research in regenerative medicine, a technical field which takes advantage of the ability of cells to differentiate and proliferate to achieve reconstruction of original biological tissues and organs, as a method for treating major injury to or loss of biological tissue and organs. Neural regeneration is a branch of this field, and research is underway toward using tubes composed of artificial materials for crosslinking between stumps in the neuron-deficient sites of patients with ablated neural tissue, to induce regeneration of the neural tissue. Such tubes are made of silicon, polyurethane, polylactic acid, polyglycolic acid, polycaprolactone or their copolymers or composites, and they are often internally coated with collagen or laminin.
For vascular regeneration there are used artificial material tubes made of polytetrafluoroethylene, polyester, polylactic acid, polyglycolic acid, polycaprolactone or their copolymers or composites, and these are also often internally coated with gelatin, albumin, collagen or laminin.
For example, Japanese Unexamined Patent Publication HEI No. 6-285150 describes artificial vessels obtained by injecting insoluble collagen into the walls of cylindrical tubes made of a fibrous substance, and then subjecting them to chemical treatment before drying.
Also, Japanese Unexamined Patent Publication HEI No. 7-148243 discloses an implant material whose matrix is a biocompatible bulky structure comprising organic fibers in a three-dimensional woven texture or knitted texture, or a composite texture obtained as a combination thereof, wherein the void fraction of the texture is preferably 20-90 vol %.
Japanese Unexamined Patent Publication HEI No. 8-294530 describes a cardiovascular restorative material characterized by insolubilizing a bioabsorbable substance attached to a porous matrix by at least one means having a physical effect of wet swelling by entanglement, heat treatment and charging.
Japanese Unexamined Patent Publication HEI No. 8-33661 describes an artificial vessel obtained by coacervation of water-soluble elastin and fixing with a crosslinking agent, either directly or after coating of gelatin or collagen and fixing with a crosslinking agent, onto the lumen surface of an artificial vessel matrix made of a synthetic resin.
Also, Japanese Unexamined Patent Publication HEI No. 9-173361 describes an artificial vessel obtained by coating of albumin onto the lumen surface of an artificial vessel matrix made of a synthetic resin, and heating thereof or further crosslinking thereof with a crosslinking agent after the heating to construct an albumin layer, followed by coacervation of water-soluble elastin thereover and fixing with a crosslinking agent.
Japanese Unexamined Patent Publication No. 2003-126125 describes an artificial vessel having a cylindrical porous artificial vessel matrix, wherein the pores of the porous artificial vessel matrix are impregnated with a gel solution containing a biofunctional substance.
These publications describe tubes having synthetic resins woven into a plain weave or knit as the matrix for an artificial vessel, nonwoven fabric tubes formed from a synthetic resin shaped into a filament and roll laminated on a mandrel, or tubes obtained by extrusion molding of a mixture of a synthetic resin and a particulate aqueous solution of sodium chloride, but all of these methods yield artificial vessel matrix tubes which lack stretchability and have unsatisfactory Young's moduli.
A modification for improving stretchability by means of a special shape is described in Japanese Unexamined Patent Publication HEI No. 5-23362, which discloses an artificial tube obtained by using multifilament yarn composed of polyester ultrafine filaments as the warp and weft yarns, and hollow weaving to yield a seamless tube which is then worked to form a bellows-shaped section.
Also, Japanese Unexamined Patent Publication HEI No. 8-71093 discloses a modification whereby pleats are added to a conical fabric prosthetic vessel whose starting material is a fiber material.
Since the aforementioned silicon, polyurethane, polytetrafluoroethylene and polyester materials lack bioabsorption properties, they are associated with problems from the standpoint of long-term safety, while compression and damage to regenerated nerves and vessels is also a concern. Also, polylactic acid, polyglycolic acid, polycaprolactone and their copolymers, while having bioabsorption properties, are problematic in terms of Young's modulus and stretchability, and can likewise lead to compression and damage to regenerated nerves and vessels. In other words, no tubes are known at the current time which exhibit superior performance from the standpoint of bioabsorption, Young's modulus and stretchability.
These problems can potentially be overcome by using composites of elastic materials such as collagen with support matrices made of polylactic acid, polyglycolic acid, polycaprolactone and their copolymers, but since conventionally known support matrices made of polylactic acid, polyglycolic acid, polycaprolactone and their copolymers lack stretchability, they counter the elastic property of the collagen and thus limit the use of such materials in the body. In other words, the currently known support matrices made of polylactic acid, polyglycolic acid, polycaprolactone and their copolymers, and composites of such support matrices with collagen, do not exhibit excellent stretchability.